OK, let's work through this together. We're starting with 155 and we're going to multiply it by 85, which means we add 155 to itself 85 times.
Step 1: 0 + 155 = 155
Step 2: 155 + 155 = 310
Step 3: 310 + 155 = 465
Step 4: 465 + 155 = 620
Step 5: 620 + 155 = 775
Step 6: 775 + 155 = 930
Step 7: 930 + 155 = 1085
Step 8: 1085 + 155 = 1240
Step 9: 1240 + 155 = 1395
Step 10: 1395 + 155 = 1550
Step 11: 1550 + 155 = 1705
Step 12: 1705 + 155 = 1860
Step 13: 1860 + 155 = 2015
Step 14: 2015 + 155 = 2170
Step 15: 2170 + 155 = 2325
Step 16: 2325 + 155 = 2480
Step 17: 2480 + 155 = 2635
Step 18: 2635 + 155 = 2790
Step 19: 2790 + 155 = 2945
Step 20: 2945 + 155 = 3100
Step 21: 3100 + 155 = 3255
Step 22: 3255 + 155 = 3410
Step 23: 3410 + 155 = 3565
Step 24: 3565 + 155 = 3720
Step 25: 3720 + 155 = 3875
Step 26: 3875 + 155 = 4030
Step 27: 4030 + 155 = 4185
Step 28: 4185 + 155 = 4340
Step 29: 4340 + 155 = 4495
Step 30: 4495 + 155 = 4650
Step 31: 4650 + 155 = 4805
Step 32: 4805 + 155 = 4960
Step 33: 4960 + 155 = 5115
Step 34: 5115 + 155 = 5270
Step 35: 5270 + 155 = 5425
Step 36: 5425 + 155 = 5580
Step 37: 5580 + 155 = 5735
Step 38: 5735 + 155 = 5890
Step 39: 5890 + 155 = 6045
Step 40: 6045 + 155 = 6200
Step 41: 6200 + 155 = 6355
Step 42: 6355 + 155 = 6510
Step 43: 6510 + 155 = 6665
Step 44: 6665 + 155 = 6820
Step 45: 6820 + 155 = 6975
Step 46: 6975 + 155 = 7130
Step 47: 7130 + 155 = 7285
Step 48: 7285 + 155 = 7440
Step 49: 7440 + 155 = 7595
Step 50: 7595 + 155 = 7750
Step 51: 7750 + 155 = 7905
Step 52: 7905 + 155 = 8060
Step 53: 8060 + 155 = 8215
Step 54: 8215 + 155 = 8370
Step 55: 8370 + 155 = 8525
Step 56: 8525 + 155 = 8680
Step 57: 8680 + 155 = 8835
Step 58: 8835 + 155 = 8990
Step 59: 8990 + 155 = 9145
Step 60: 9145 + 155 = 9300
Step 61: 9300 + 155 = 9455
Step 62: 9455 + 155 = 9610
Step 63: 9610 + 155 = 9765
Step 64: 9765 + 155 = 9920
Step 65: 9920 + 155 = 10075
Step 66: 10075 + 155 = 10230
Step 67: 10230 + 155 = 10385
Step 68: 10385 + 155 = 10540
Step 69: 10540 + 155 = 10695
Step 70: 10695 + 155 = 10850
Step 71: 10850 + 155 = 11005
Step 72: 11005 + 155 = 11160
Step 73: 11160 + 155 = 11315
Step 74: 11315 + 155 = 11470
Step 75: 11470 + 155 = 11625
Step 76: 11625 + 155 = 11780
Step 77: 11780 + 155 = 11935
Step 78: 11935 + 155 = 12090
Step 79: 12090 + 155 = 12245
Step 80: 12245 + 155 = 12400
Step 81: 12400 + 155 = 12555
Step 82: 12555 + 155 = 12710
Step 83: 12710 + 155 = 12865
Step 84: 12865 + 155 = 13020
Step 85: 13020 + 155 = 13175

So, 155*85 = 13175